high CVSS 7.8 EPSS <0.1%

CVE-2023-52836·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: locking/ww_mutex/test: Fix potential workqueue corruption In some cases running with the test-ww_mutex code, I was seeing odd behavior where sometimes it seemed flush_workqueue was returning before all the work threads were finished. Often this would cause strange crashes as the mutexes would be freed while they were being used. Looking at the code, there is a lifetime problem as the controlling thread that spawns the work allocates the "struct stress" structures that are passed to the workqueue threads. Then when the workqueue threads are finished, they free the stress struct that was passed to them. Unfortunately the workqueue work_struct node is in the stress struct. Which means the work_struct is freed before the work thread returns and while flush_workqueue is waiting. It seems like a better idea to have the controlling thread both allocate and free the stress structures, so that we can be sure we don't corrupt the workqueue by freeing the structure prematurely. So this patch reworks the test to do so, and with this change I no longer see the early flush_workqueue returns.

Severity
high
Software
Kernel
Fixed in
6.6.3
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at <0.1% — higher than 3% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Read the two together. CVE-2023-52836 scores 7.8 on CVSS, so a successful attack would be serious — but at <0.1%, almost nobody is currently attempting it. That is a different situation from a flaw under mass exploitation, and it is usually the difference between patching on your next maintenance window and patching tonight.

Affected versions

From: 6.6

Until: 6.6.3

Fixed in: 6.6.3

How to fix this CVE

Update your Linux kernel to version 6.6.3 or later to resolve a memory lifetime issue in the ww_mutex test code that could cause workqueue corruption and system crashes. The vulnerability stems from premature deallocation of synchronization structures while the kernel's work queue is still processing them. Ensure your system is running a patched kernel version and reboot to apply the security update.

sudo dnf update kernel kernel-devel

Defensia detects this vulnerability

How to check if you are affected

  1. Step 1: Check your current kernel version with `uname -r` and compare against 6.6.3; if you see 6.6.0 through 6.6.2, you are vulnerable
  2. Step 2: Verify if the ww_mutex test module is loaded by running `lsmod | grep ww_mutex` or check kernel configuration with `grep CONFIG_WW_MUTEX_SELFTEST /boot/config-$(uname -r)`
  3. Step 3: Search system logs for workqueue-related crashes using `sudo journalctl -S -1h | grep -E '(workqueue|ww_mutex|work_struct|flush_workqueue|kernel crash)'`
  4. Step 4: After patching and reboot, verify the fixed version is active with `uname -r` and confirm it shows 6.6.3 or later

FAQ

What is CVE-2023-52836?

CVE-2023-52836 is a memory safety vulnerability in the Linux kernel's ww_mutex test suite where work queue structures are freed prematurely while the work queue is still processing them, leading to use-after-free conditions and potential kernel crashes.

Is CVE-2023-52836 being actively exploited?

No, this vulnerability is not listed on the CISA Known Exploited Vulnerabilities catalog and no public exploits are available. However, it can cause denial of service through system crashes if triggered.

What versions of Kernel are affected by CVE-2023-52836?

Linux kernel versions 6.6.0 through 6.6.2 are affected. The vulnerability was fixed in kernel version 6.6.3.

How do I check if my server is vulnerable to CVE-2023-52836?

Run `uname -r` to display your kernel version. If the output shows any version from 6.6.0 to 6.6.2, your system is vulnerable and requires an immediate kernel update.

Does Defensia detect CVE-2023-52836?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If the Linux kernel is installed on a monitored server, CVE-2023-52836 will appear in your dashboard with remediation steps.

Related Kernel CVEs

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CVE-2026-52955CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: libceph: Fix potential out-of-bounds access in crush_decode() A message of type CEPH_MSG_OSD_MAP containing a crush map with at least one bucket has two fields holding the bucket algorithm. If the values in these two fields differ, an out-of-bounds access can occur. This is the case because the first algorithm field (alg) is used to allocate the correct amount of memory for a bucket of this type, while the second algorithm field inside the bucket (b->alg) is used in the subsequent processing. This patch fixes the issue by adding a check that compares alg and b->alg and aborts the processing in case they differ. Furthermore, b->alg is set to 0 in this case, because the destruction of the crush map also uses this field to determine the bucket type, which can again result in an out-of-bounds access when trying to free the memory pointed to by the fields of the bucket. To correctly free the memory allocated for the bucket in such a case, the corresponding call to kfree is moved from the algorithm-specific crush_destroy_bucket functions to the generic crush_destroy_bucket().
CVE-2026-53384CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: serial: 8250_dw: unregister 8250 port if clk_notifier_register() fails dw8250_probe() registers the 8250 port via serial8250_register_8250_port() and then, if the device has a clock, registers a clock notifier. If clk_notifier_register() fails, probe returns the error but leaves the 8250 port registered. The matching serial8250_unregister_port() lives in dw8250_remove(), which is not called when probe fails, so the port slot stays occupied until the device is rebound or the system is rebooted. The devm-allocated driver data is freed while the port still references it (via the saved private_data and serial_in/serial_out callbacks), so any access to that port slot before a rebind is a use-after-free hazard. Unregister the port on the clk_notifier_register() error path.
CVE-2026-52931CVSS 9.8In the Linux kernel, the following vulnerability has been resolved: batman-adv: tp_meter: avoid use of uninit sender vars batadv_tp_recv_ack() and batadv_tp_stop() are only valid for tp_vars in the BATADV_TP_SENDER role. When called with a BATADV_TP_RECEIVER role, it proceeds to read sender-only members that were never initialized, leading to undefined behavior. This can be triggered when a node that is currently acting as a receiver in an ongoing tp_meter session receives a malicious ACK packet. Guard against this by checking tp_vars->role immediately after the lookup and bailing out if it is not BATADV_TP_SENDER, before any of those members are accessed.
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References

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